Electrical resistor units



Feb. 17, 1959 c. w. KUHN ET A1. 2,874,258

ELECTRICAL RESISTOR UNITS Original Filed Aug. 27. 1952 2 Sheets-Sheet 1 O 364--2 AO 5| Inventor: 44v N44 Va/rence I/l/,Ka/lz Fue. 5 5? Feb. 17, 1959 C, W, KUHN Ef AL .2,874,258

ELECTRICAL RESISTOR UNITS Original Filed Aug. 27, 1952 2 Sheetsheet 2 lo 4 la l5 I 59 4o ,go /ww 14"* nz 5" l2 lo v Y n! 4' 'f' f, 03W, l l,

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[zz Ven for; Clarence IA/T (a/fz Poef 0, Pern/ze gu y l?, Radley United States Patent O ELECTRICAL nEsIsroR UNITS Clarence W. Kuhn and Robert O. Perrine, Wauwatosa,

and Guy R. Radley, Milwaukee, Wis., assignors to Cutler-Hammer, Inc., Milwaukee, Wis a corporation of Delaware l Original application August 27, 19.52, Serial No. 306,574. Divided and this application February 27, 1956, Serial No. 567,791

16 Claims. (Cl. 201-74) This invention relates to improvements in resistors, particularly the type used in the dynamic braking of electric motors.

This is a divisional application of application Serial No. 306,574, led August 27, 1952.

Resistors of this type are described and claimed in the Kuhn and Welch Patent No. 2,680,178, granted June 1, 1954, for Resistor Unit and Method of Making the Same, and assigned to the same assignee as the present application. The capacity of such units is limited, however, by overheating occurring in the loops or reilexes of the grid and in the insulators where such loops are supported.

It is the object of this invention therefore to provide a resistor in which overheating in the loops of the grid and the insulator where such loops are supported is prevented and the capacity of the resistor increased Without appreciable increase in physical dimensions.

This object is obtained by supporting the grid by brackets which hold the loops away from the insulators and in the cooling air stream so that heat will be dissipated from the loops as readily as from the lengths between the loops and hence prevent any damaging overheated areas in such loops or insulators.

The novel features which are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the vfollowing description of specic embodiments when read in connection with the accompanying drawings in which:

Figure 1 is a horizontal plane sectional view of a rst 'form of resistor embodying the present invention;

Fig. 2 is an enlarged fragmentary sectional view taken on the line 2 2 of Fig. l;

Fig. 3 is a sectional view taken on the line 3 3 of r Fig. 2;

Fig. 4 is an enlarged sectional view similar to Fig. 3 of a second form of resistor embodying the present invention;

Fig. 5 is an enlarged sectional view similar to Fig. 2 of a third form of resistor embodying the present invention; f

Fig. 6 is a sectional view taken on the line 6 6 of Fig. 5;

Fig. 7 is a fragmentary horizontal plane sectional view of a fourth form of resistor embodying the present invention;

Fig. 8 is an enlarged fragmentary sectional view taken on the line 8 8 of Fig. 7;

Fig. 9 is a fragmentary horizontal plane sectional view of a fifth form of resistor embodying the present invention;

Fig. 10 is an enlarged fragmentary sectional view taken on the line 10 10 of Fig. 9;v

Fig. 11 is an enlarged fragmentary sectional view taken on the line 11-11 of Fig. 8;

ice

Fig. 12 is an enlarged fragmentary taken on the line 12-12 of Fig. 8;

Fig. 13 is an enlarged fragmentary taken on the line 13 13 of Fig. 8;

Fig. 14 is an enlarged fragmentary taken on the line 14 14 of Fig. 8;

Fig. 15 is an enlarged fragmentary taken on the line 15 15 of Fig. 8;

Fig. 16 is an enlarged fragmentary sectional view taken on the line 16 16 of Fig. 10, part being broken away for clarity;

Fig. 17 is an enlarged fragmentary sectional view taken on the line 17 17 of Fig. 10; and

Fig. 18 is an enlarged fragmentary sectional view similar to Fig. 17 of a sixth form of resistor embodying the present invention.

In all of the forms of the resistor shown and described the metal frame has side channels 10 and 12, end plates 14 and 16, pressure plate 32 and compression springs 30 all identical in structure and function with the frame disclosed in the aforementioned Patent No. 2,680,178. The grid 44 is of the same construction as that described and claimed in said Patent No. 2,680,178. In the first three forms (Figs. l to 6, inclusive) the insulators 34 are the same as those of said Patent No. 2,680,178 and have spaced grooves 36 adapted to hold the brackets of the grid 44. As in said patent a sheet of mica 40 or other like insulating material is placed between the metal frame and the insulators.

In order to prevent overheating of the loops or reflexes 46 and of the insulators, the loops 46 are supported by metal clips, brackets or hangers extending between the insulators and loops. These brackets are long enough to keep the loops 46 out of heat conducting contact with the insulators and to place such loops in the same cooling air stream as the lengths 48. This avoids heat insulation of the loops by the insulator and enables the loops to lose heat as rapidly as the remainder of the grid. It also prevents direct transfer of heat from the highly heated loops to the insulators at the place of support. Such heat as is transferred to the insulators is the result of direct radiation from the loop and by conduction through such brackets. The heat so transferred is not, however, suflicient to injure the insulation.

In the first, second and third forms aforementioned the insulators 34 and grooves 36 are of the same de* sign as those of said Patent No. 2,680,178. However, the use of brackets lessens the effective length of the lengths 48 and in some applications it may be necessary to slightly lengthen the end plates 14 and 16 to produce a comparable resistance.

In the rst form (Figs. 1, 2 and 3) a bracket 51 consisting of a U-shaped metal piece has legs straddling and spot welded to the loop 46 and a bridge portion seated in the groove 36. Substantially no current is carried by the bracket 51 and hence the only heat generated therein is that caused by conduction from the loop 46. Hence the insulator 34 will not be excessively heated and the loop 46 being held out away from the insulator in the cooling air stream for the grid 44 will not get hotter than the lengths 48.

The second form (Fig. 4) is the same as the lirst form except that the bracket 51 is secured by rivets 53 to the sides of the loop 46. This eliminates the spot welding and the attendant heat treatment and also decreases the conduction of heat from the grid to the bracket.

The bracket 55 of the third form (Figs. 5 and 6) consists of a strip of metal having only one leg spot welded or riveted to one side of the loop 46. Such strip is offset as shown so that its outer end is subsectional view sectional view sectional view sectional view ,stantially in alinement with the center of the loop 46.

garages With such outer end positioned in a groove 36 the loop 46 will be positioned in proper alinement with such groove and the loop 46 will be held in the same cooling air stream as the remainder of the grid. The only heat in the bracket 55 will be that received ,byl conduction from` the grid 44;.there being no current ow in such bracket.

In the fourth, fifth and sixthforms the insulators are not of the same design as those of Patent No. 2,680,178. However, the peripheral shape is substantially the same so that the insulators of these forms of the invention will lit in the same frame as the other forms herein disclosed. In these last three forms, like the first, second and third forms, the loops 46 are held spaced from the insulator and are in the cooling air stream. The common characteristic of the fourth, fth and sixth forms is the use of a bracket in which the loop 46 of the grid removably fits and is held in place by pressure rather than by riveting or spot welding. This cuts down assembly cost without sacrifice of efficiency.

In the fourth form (Figs. 7, 8, and ll to 15, inclusive) the insulators have spaced pockets 37 for frictionally holding the loop supporting brackets. Each of these pockets as is seen at Fig. 12 has a central vertical ridge 39 which projects inwardly of the pocket from one side and two end abutments 41 projecting inwardly of the pocket from the side opposite the ridge 39. To facilitate the assembly of the bracket in the pocket the central part of the side opposite ridge 39 may be cut away as shown at 43 (Fig. l5), and on each side of ridge 39 the pocket may be cut away as indicated at 4S. All these cutaway portions slope inwardly and downwardly so that at the top of the pocket the opening is bow shaped to permit the bracket to readily enter the pocket when flexed. The back of insulators 35 may have slots 33 positioned midway of the pockets 37 to provide a more uniform cross section with consequent even heat dissipation and better circulation of air around the back ofsuch insulators.

The loop supporting bracket has a mounting bar 57 with lateral feet 59. This bar is flexed or bowed in order to fit it into the opening of the pocket. As the bracket i-s pressed down into the pocket the ridge 39 and the abutments 41 will keep such bar sprung against its inherent resiliency and thus provide a frictional force holding the bracket in place. The bracket has three loop supporting arms 61, the outer two of which are bent to one side and the center one of which is bent to the other side of the bracket to engage the loop from opposite sides. The outer arms have inwardly laterally projecting tabs 63 which engage the opposite edges of the loop 46 to prevent edgewise displacement thereof.

To assemble this modification the brackets are preferably iirst'inserted and press fitted into the pockets of the insulator and then the grid is assembled in the same manner as set forth in said Patent No. 2,680,178.

ln the fifth form (Figs. 9, l0, 16 and l7) loop holding brackets 65 have portions molded into the insulators67 and are not removable therefrom. Such portions rnay be shaped as shown in Fig. l() or have any other irregular shape which provides good gripping engagement between the insulating material and the metal bracket. The brackets 65 have projecting ears 69 which iit in notches 71 on the loops 46 to properlyl anchor the grid in place. Assembly may be accomplished in the same way as the fourth form aforementioned.

Instead of molding the loop holding bracket into the insulator, the sixth form (Fig. 18) uses a bracket '73 which has a mounting leg 75 resting flatly against the inner face of an insulator 77 and held in place by rivets 79. In other respects the bracket '73 is the same as bracket 65 and holds the loop 46 in the same way.

Althoughseveral embodiments of the` invention are shownY andydescribedherein it will be understood that this application is intended to cover such other changes or modifications as come with the spirit of the inven-v tion or scope of the following claims.

We claim:

l. A resistor unit adapted for use with forced ventilation, said resistor unit having oppositely positioned insulators with grooves adapted to receive brackets for supporting the loops of a ribbon type grid resistor, a ribbon type grid resistor having loops, and brackets received in said grooves and frictionally engaging said loops to provide sliding engagement therebetween, said brackets being long enough to keep said loops out of contact with said insulators and in the same cooling air ream as the remainder of said grid resistor.

2. A resistor unit as claimed in claim l in which said brackets consist of strips ofmetal having at least one end supporting said loops, said metal strips being seated in said grooves to thereby effect support of said grid resistor.

3. A resistor unit adapted for use with forced ventilation, said resistor unit lhaving an insulator, a pocket in said insulator adapted tov receive and frictionally holdv therein a loop mounting bracket `against normal shock conditions, a loop mounting bracket having a mounting bar pressed into said pocket, said ,bracket having loop supporting arms adapted to resiliently engage and hold a loop of a ribbon type grid resistor, said resilient engagement permitting sliding movement between said loop and said bracket, and a ribbon type grid resistor having a loop positioned in said arms and spaced from said insulator by said bracket.

4. A resistor unit as claimed in claim 3 in which said pocket has a vertical ridge projecting inwardly from one wall thereof and two end abutments projecting inwardly from the opposite wall thereof, said ridge and abutments engaging said mounting bar to flex said bar against the inherent resiliency thereof to provide frictional holding forces.

5. A resistor unit as claimed in claim 4 in which said pocket has cut-away portions on opposite sides to provide a bow-shaped Vopening at the top thereof facilitating entry of said mounting bar.

6. A resistor unit as claimed in claim 3 in which said loop supporting arms have inwardly projecting tabs adapted to engage the edges of said loop to restrain edgewise displacement thereof.

7. In combination with an insulator support and an electrical resistor having abend therein, a member having a plurality of diverging fingers cradling said bend, and means for fastening the member and said insulator support together so that said bend is cradled in a location removed from said insulator support, said means including a prolongation of said member adapted to be. inserted in a slot in said insulator support, said slot havingma'ted surfaces spaced to frictionally engage said prolongation and retain it therein. Y

8. ln combination with aninsulator support andan electrical resistor having a bend therein, a member having a plurality of diverging fingers cradling said bend, and means for fastening the member and said insulator support together so that said bendis cradled in a location removed from said insulator support, said means including a prolongation of said member adapted to be inserted in a slot in said insulatorsupport, said slot having mated concave and .convex surfaces spaced t'o frictionally engage each side of said prolongation and retain it therein. i

9. A compact resistor unit adapted for use with forced ventilation, said resistor unit having oppositely positioned insulators, a ribbon type resistor grid having loops and positioned between said insulators, grid supporting means rigidly secured to said insulators to prevent relative movement therebetween under `normal, shock, conditions, said means frictionally engagingv said loops to permit expansion and contraction of said grid While maintaining continued supporting engagement therebetween under said shock conditions.

10. A resistor unit as claimed in claim 9 in which said means includes brackets interposed between said insulators and said loops to hold said loops spaced from and between said insulators.

l1. In combination with an insulator support and an electrical resistor having a bend therein, a member having a preformed socket which receives and supports said bend, said socket being formed by a cutout portion leaving spaced projections defining the opposite sides of said socket, notches on opposite sides of said resistor for slidably receiving said projections to provide for expansion and contraction of said resistor while preventing lateral movement of the latter under shock conditions, said member being provided with means for fastening the same to said insulator support so that said bend is supported remote from said insulator support.

l2. The combination defined in claim ll, wherein said fastening means comprises an extension opposite said socket rigidly secured to said insulator support.

13. The combination defined in claim 12, wherein said extension is molded in said insulator support.

14. The combination defined in claim l2, together with means for removably securing said extension to said insulator support.

l5. A resistor unit exposed to cooling media, said resistor unit having oppositely positioned insulators, a ribbon type resistor grid having loops and positioned between said insulators, grid supporting means for spacing said loops from said insulators, means for mounting said grid supporting means to said insulators to prevent relative movement therebetween under normal shock conditions, and means on said grid supporting means for frictionally engaging said loops to permit expansion and contraction of said grid while maintaining continued supporting engagement therebetween under said shock conditions.

16. In a resistor unit exposed to cooling media, a ribbon type resistor element having a loop therein, an insulator member, a bracket for supporting said loop spaced from said insulator member so that said loop is exposed to cooling media, means for mounting said bracket to said insulator member to withstand normal shock conditions, and means on said bracket for frictionally and slidably engaging said loop to permit expansion and contraction of said resistor element while preventing relative lateral movement therebetween under heat and shock conditions.

No references cited. 

